A phenolate-induced trans influence: crystallographic evidence for unusual asymmetric coordination of an alpha-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands

Inorg Chem. 2005 May 2;44(9):3070-9. doi: 10.1021/ic048835o.

Abstract

Three mononuclear ternary complexes of iron(III) with an alpha-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L] x MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-N(pyridyl) bond trans to the phenolate oxygen is 0.133 A longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L'-L')L] x MeCN (L'-L' = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (p(pi)) --> iron(III) (d(pi*)) (lambda(max) approximately 500 nm, epsilon approximately 3000 M(-1) cm(-1)) and phenolate (p(pi)) --> iron(III) (d(sigma*) (lambda(max) approximately 320 nm, epsilon approximately 5200 M(-1) cm(-1)). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Crystallography, X-Ray
  • Dioxygenases / chemistry*
  • Dioxygenases / metabolism
  • Electron Spin Resonance Spectroscopy
  • Ferric Compounds / chemical synthesis
  • Ferric Compounds / chemistry*
  • Indicators and Reagents
  • Iron / chemistry*
  • Ligands
  • Models, Molecular
  • Molecular Conformation
  • Molecular Structure
  • Phenols / chemistry
  • Spectrophotometry, Infrared

Substances

  • Ferric Compounds
  • Indicators and Reagents
  • Ligands
  • Phenols
  • Iron
  • Dioxygenases